Bouncing is when two particularly amusing individuals coordinate impeccably to deliver outstanding humour, by alternating in conversation and playing off each others 'gags'.
Girl 2: I know they've been bouncing off each other all night
Girl 3: Im going to see if i can interupt them and try and get with them
Girl 4: Not if i do first
Girl 2: Lets just all get with them simultaneously
Other three girls: you always were the brains of the group